Conventionally, electronic watermarking techniques fall into a category wherein a theoretical electronic watermarking method is applied unchanged for a variety of products, and no truly practical technique has been provided that can prevent the analyzation of an embedding algorithm. As an example, an electronic watermarking technique for digital data, an embedding and detection method used for a frequency domain, is disclosed in U.S. Pat. No. 5,687,236. According to this conventional electronic watermarking technique, embedded additive information is detected so that it can be synchronized with information (embedding start information) indicating the start of embedding. With this method, however, in addition to the additive information that originally is embedded, a synchronization signal is provided that must be used when detecting the embedded additive information. This signal must, therefore, be detected first, and accordingly, additional time is required for this purpose. Further, when a third party, with larcenous intent, detects a synchronization signal, that party can easily analyze and extract all the embedded information. Therefore, it is generally acknowledged that a need exists for a practical and robust electronic watermarking technique.